The present invention relates to bumpers and, more particularly, to bumpers comprised of a rigid rear support and a deformable front hollow section with freely extending parallel shank portions fixed on the rigid support. Reenforcing ribs extend between the shanks with their free edges arranged opposite, and at least approximately parallel to the front portion of the rigid support.
Bumpers of this kind, which may be used for motor vehicles and also for the protection of stationary objects, as on bumping posts or the like, are disclosed, for example, in the German patent publication (Offenlegungsschrift) No. 2,433,138. These bumpers operate in such a way that, relatively shortly after the commencement of an impact, the free edges of the reenforcing ribs come to bear against the front surface of the rigid support, thereby essentially determining the bumper's energy absorbing characteristic. The wall thickness of the reenforcing ribs is therefore one of the factors affecting this energy absorbing characteristic.
Because the shank portions of the deformable front hollow section are fixed on the rigid support, these portions have a tendency to bend outwardly on impact, producing tensile stresses within the material of the reenforcing ribs. As tests have shown, these tensile stresses may cause cracks to form in the reenforcing ribs in the transition region where the free edges of the reenforcing ribs extend into the shank portions of the deformable front hollow section.
It is an object of the present invention to provide a bumper of the type described above in which the aforementioned phenomenom of crack formation is substantially reduced without changing or impairing the bumper's energy absorbing characteristics.
It is an object of the present invention to provide a bumper of the type described above in which crack formation is substantially reduced without any increase in the wall thickness of the reenforcing ribs.